Polishing pad having a sealed pressure relief channel

ABSTRACT

The present invention provides a chemical mechanical polishing pad comprising a window formed in the polishing pad, the window having a void provided on a side thereof. The invention further provides a pressure relief channel provided in the polishing pad from the void to a periphery of the polishing pad. In addition, a membrane is provided in the channel to prevent contamination of the void.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application Ser.No. 60/706,873 filed Aug. 10, 2005.

BACKGROUND OF THE INVENTION

The present invention relates to polishing pads for chemical mechanicalplanarization (CMP), and in particular, relates to polishing pads havingreduced stress windows formed therein for performing optical end-pointdetection. Further, the present invention relates to polishing padshaving a sealed pressure relief channel to reduce stress on the windowsand prevent contamination of the window area.

In the fabrication of integrated circuits and other electronic devices,multiple layers of conducting, semiconducting and dielectric materialsare deposited on or removed from a surface of a semiconductor wafer.Thin layers of conducting, semiconducting, and dielectric materials maybe deposited by a number of deposition techniques. Common depositiontechniques in modem processing include physical vapor deposition (PVD),also known as sputtering, chemical vapor deposition (CVD),plasma-enhanced chemical vapor deposition (PECVD), and electrochemicalplating (ECP).

As layers of materials are sequentially deposited and removed, theuppermost surface of the wafer becomes non-planar. Because subsequentsemiconductor processing (e.g., metallization) requires the wafer tohave a flat surface, the wafer needs to be planarized. Planarization isuseful in removing undesired surface topography and surface defects,such as rough surfaces, agglomerated materials, crystal lattice damage,scratches, and contaminated layers or materials.

Chemical mechanical planarization, or chemical mechanical polishing(CMP), is a common technique used to planarize substrates, such assemiconductor wafers. In conventional CMP, a wafer carrier is mounted ona carrier assembly and positioned in contact with a polishing pad in aCMP apparatus. The carrier assembly provides a controllable pressure tothe wafer, pressing it against the polishing pad. The pad is moved(e.g., rotated) relative to the wafer by an external driving force.Simultaneously therewith, a chemical composition (“slurry”) or otherpolishing solution is provided between the wafer and the polishing pad.Thus, the wafer surface is thus polished and made planar by the chemicaland mechanical action of the pad surface and slurry.

An important step in planarizing a wafer is determining an end-point tothe process. Accordingly, a variety of planarization end-point detectionmethods have been developed, for example, methods involving opticalin-situ measurements of the wafer surface. The optical techniqueinvolves providing the polishing pad with a window for selectwavelengths of light. A light beam is directed through the window to thewafer surface, where it reflects and passes back through the window to adetector (e.g., a spectrophotometer). Based on the return signal,properties of the wafer surface (e.g., the thickness of films) can bedetermined for end-point detection.

Roberts, in U.S. Pat. No. 5,605,760, discloses a polishing pad having awindow formed therein. In Roberts, a window is cast and inserted into aflowable polishing pad polymer. This polishing pad may be utilized in astacked configuration (i.e., with a subpad) or used alone, directlyadhered on the platen of a polishing apparatus with an adhesive. Ineither case, there is a “void” or space that is created between thewindow and the platen. Unfortunately, during polishing, undue stress isapplied to the window from the pressure that is generated in the voidand may cause unwanted residual stress deformations (e.g., “bulges” or“caving-in”) in the window. These stress deformations may result innon-planar windows and cause poor end-point detection, defectivity andwafer slippage.

Hence, what is needed is a polishing pad having a reduced stress windowfor robust end-point detection or measurement during CMP over a widerange of wavelengths.

STATEMENT OF THE INVENTION

In a first aspect of the present invention, there is provided a chemicalmechanical polishing pad comprising: a window formed in the polishingpad, the window having a void provided on a side thereof; a pressurerelief channel provided in the polishing pad from the void to aperiphery of the polishing pad; and a membrane provided in the channelto prevent contamination of the void.

In another aspect of the present invention, there is provided a chemicalmechanical polishing pad comprising: a polishing layer having a windowformed therein, the window being exposed to a void on a side thereof; apressure relief channel provided in the polishing layer from a portionof the void-exposed side of the window to a periphery of the polishinglayer; and a membrane provided in the channel to prevent contaminationof the void.

In another aspect of the present invention, there is provided a chemicalmechanical polishing pad comprising: a polishing layer overlying abottom layer, and an adhesive layer disposed between the polishing layerand the bottom layer; a window formed in the polishing layer, the windowbeing exposed to a void on a side thereof; a pressure relief channelprovided in the adhesive layer from the void to a periphery of theadhesive layer; and a membrane provided in the channel to preventcontamination of the void.

In another aspect of the present invention, there is provided a chemicalmechanical polishing pad comprising: a polishing layer overlying abottom layer, and an adhesive layer disposed between the polishing layerand the bottom layer; a window formed in the polishing layer, the windowbeing exposed to a void on a side thereof; a pressure relief channelprovided in the bottom layer from the void to a periphery of the bottomlayer; and a membrane provided in the channel to prevent contaminationof the void.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a polishing pad having a pressure relief channel ofthe present invention including a membrane;

FIG. 2A illustrates a sectional view along line I-II of the polishingpad of FIG. 1;

FIG. 2B illustrates another embodiment of a sectional view along lineI-II of the polishing pad of FIG. 1;

FIG. 3 illustrates another embodiment of a polishing pad having apressure relief channel of the present invention;

FIG. 4 illustrates another embodiment of a polishing pad having apressure relief channel of the present invention; and

FIG. 5 illustrates a CMP system utilizing the polishing pad of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, a polishing pad 1 of the present invention isshown. Polishing pad 1 comprises a polishing layer 4 and an optionalbottom layer 2. Note, polishing layer 4 and bottom layer 2 mayindividually serve as a polishing pad. In other words, the presentinvention may be utilized in the polishing layer 4 alone, or in thepolishing layer 4 in conjunction with the bottom layer 2, as a polishingpad. The bottom layer 2 may be made of felted polyurethane, such asSUBA-IV™ pad manufactured by Rohm and Haas Electronic Materials CMP Inc.(“RHEM”), of Newark, Del. The polishing layer 4 may comprise apolyurethane pad (e.g., a pad filled with microspheres), such as, IC1000™ pad by RHEM. Polishing layer 4 may optionally be texturized asdesired. A thin layer of pressure sensitive adhesive 6 may hold thepolishing layer 4 and the bottom layer 2 together. The adhesive 6 may becommercially available from 3M Innovative Properties Company of St,Paul, Minn.

Polishing layer 4 has a transparent window 14 provided over the bottomlayer 2 and the pressure sensitive adhesive 6. Polishing layer 4 mayhave a thickness T between 0.70 mm to 2.65 mm. Note, window 14 isprovided over the void 10 that creates a pathway for the signal lightutilized during end-point detection. Accordingly, laser light from alaser spectrophotometer (not shown) may be directed through the void 10and transparent window block 14, and onto a wafer or substrate tofacilitate end-point detection. Note, although the present invention isdescribed with reference to a polishing pad having an integrally formedwindow, the invention is not so limited. For example, the entirepolishing layer 4 may be transparent (“clear pad”) and the void,including pressure, may be created at any point where, for example, thelaser spectrophotometer is placed. In other words, the present inventionis applicable to a window-less pad. Also, although the present inventionis described with respect to end-point detection through a window 14utilizing a laser spectrophotometer, the invention is not so limited.For example, the polishing layer 4 may be suitably adapted toaccommodate other end-point detection methods, for example, measuringthe resistance across a polishing surface of the wafer.

In an exemplary embodiment of the invention, polishing pad 1 comprises apressure relief channel 11, including a membrane 12, having an inlet 11a and an outlet 11 b. The pressure relief channel 11 extends from aportion of the window 14, on side 14 a that is exposed to the pressurecreated in void 10, to a periphery 4 a of the polishing pad 1, inparticular, a periphery 4 a of the polishing layer 4. Hence, pressurethat is generated in the void 10 during the polishing operation may beevacuated through the membrane 12, and inlet 11 a and outlet 11 b ofpressure relief channel 11. In other words, any pressure that isgenerated in void 10 does not materially affect the transparent window14 since the pressure escapes through the pressure relief channel 11.Therefore, the transparent window 14 is not stressed or deformed due tothe pressure build-up and accurate end-pointing is facilitated. Note,although the invention is described here as having a single pressurerelief channel, the invention is not so limited. For example, there maybe more than one pressure relief channel provided in the polishing layer4. Alternatively, a single or multiple pressure relief channels may beprovided in each of the separate layers (i.e., the adhesive layer andthe bottom layer) or any combinations thereof without departing from thescope of the invention. In addition, although the invention is describedas having a pressure relief channel that extends to the periphery of thepolishing pad, the invention is equally applicable to a polishing padhaving a pressure relief channel that extends from the void 10 to thepolishing surface of the polishing layer 4. Alternatively, the polishingpad may have a pressure relief channel (including membrane 12) thatextends from the void 10, through the window 14, to the polishingsurface of the polishing layer 4.

Advantageously, membrane 12 prevents contamination (e.g. slurry flow)through the channel and into the void area. Membrane 12 is impermeableto contaminants, for example, slurry, but allows heat and pressure toescape from the void area and through the channel. In essence, membrane12 acts as a filter, allowing certain undesired items to be releasedwhile preventing certain other undesired items from entering.

Membrane 12 of the polishing pad of the present invention may bemanufactured from polyester, polyethylene, polypropylene,fluoropolymers, polyurethane foamed films, silicone, nylon, silk, wovenmaterials and polyethylene terephthalate (PET), or any otherbiocompatible material. In one embodiment of the present invention, themembrane material is a fluoropolymer, in particular,polytetrafluoroethylene (PTFE). More preferably, the membrane materialis expanded polytetrafluoroethylene (ePTFE) having a node-fibrilstructure (e.g., GORE-TEX® membrane vents, manufactured by W. L. Goreand Associates, Inc., Elkton, Md.). Other commercially availablemembranes include modified acrylic copolymer membranes (VERSAPOR® Rmembranes, manufactured by Gelman Sciences, Ann Arbor, Mich.), modifiedpolyvinylidene fluoride (DURAPEL® membranes, manufactured by theMillipore Corporation, Bedford, Mass.) and other microporous materialsthat are commonly used to relieve pressure from enclosures.

The membrane used in the present invention may be manufactured from thinfilms of ePTFE that are each approximately 0.0025 to 0.025 mm thick.From 1 to about 200 plys (layers) of ePTFE film may be stacked up andlaminated to one another to obtain a membrane with the desiredmechanical and structural properties. An even number of layers arepreferably stacked together (e.g., 2, 4, 6, 8, 10, etc.), withapproximately 2 to 20 layers being desirable. Cross-lamination occurs byplacing superimposed sheets on one another such that the film drawingdirection, or stretching direction, of each sheet is angularly offset byangles between 0 degrees and 180 degrees from adjacent layers or plies.Since the base ePTFE is thin, as thin as 0.0025 mm thick, superimposedfilms can be rotated relative to one another to improve the mechanicalproperties of the membrane. In one embodiment of the present inventionthe membrane is manufactured by laminating 8 plies of ePTFE film, eachfilm ply being 0.0125 mm thick. In another embodiment of the presentinvention the membrane is manufactured by laminating 4 plies of ePTFEfilm, each film ply being 0.0125 mm thick. The laminated ePTFE sheetsare then sintered together at temperatures of about 370° C., undervacuum to adhere the film layers to one another.

Advantageously, the pressure relief channel 11 may be formed by, forexample, milling the channel utilizing a computer-numerically controlledtool (“cnc tool”), laser cutting, knife cutting, pre-molding the padwith the channel in place or melting/burning the channel into the pad.Most preferably, the pressure relief channel 11 is formed by milling orlaser cutting the channel. Thereafter, membrane 12 may be inserted intothe channel, as desired. Depending on the location of the channel (i.e.,polishing layer, adhesive layer or the bottom layer) the membrane 12 maybe provided in the channel 11 at various steps during the manufacturingprocess of the polishing pad. In addition, the membrane 12 may belocated anywhere along the channel 11, as desired.

Referring now to FIG. 2A, a sectional view along line I-II of polishinglayer 4 of FIG. 1 is provided. In this embodiment, the pressure reliefchannel 11 has a semi-circular profile. Note, however, that theparticular shape of the profile of the pressure relief channel 11 may bevaried without departing from the scope of the invention. For example,the profile of the pressure relief channel 11 may be semi-square orsemi-rectangular. In addition, the pressure relief channel 11 has apredetermined width W and depth D. Preferably, the width W is between0.70 mm to 6.50 mm. More preferably, the width W is between 0.80 mm to4.00 mm. Most preferably, the width W is between 0.85 mm to 3.50 mm. Inaddition, the pressure relief channel 11 preferably has a depth Dbetween 0.38 mm to 1.53 mm. More preferably, the depth D is between 0.50mm to 1.27 mm. Most preferably, the depth D is between 0.55 mm to 0.90mm. Also, the width W and depth D may be varied along the length of thepressure relief channel 11 to facilitate pressure evacuation. Forexample, the width W may be narrower near the window 14 as compared tothe periphery 4 a, creating a capillary action to prevent slurrycontamination.

Referring now to FIG. 2B, an alternative embodiment of the pressurerelief channel 11 of the present invention is provided. Similar featuresas in FIG. 2A are denoted by the same numerals. Here, the profile of thepressure relief channel 11 is semi-rectangular. As discussed above withreference to FIG. 2A, the pressure relief channel 11 has a predeterminedwidth W and depth D. In addition, the width W and depth D may be variedalong the length of the pressure relief channel 11 to facilitatepressure evacuation.

Referring now to FIG. 3, there is provided another embodiment of apolishing pad having a pressure relief channel of the present invention.Similar features as in FIG. 1 are denoted by the same numerals. Here, apolishing pad 3 is provided comprising a pressure relief channel 31,having an inlet 31 a and an outlet 31 b, formed in the adhesive 6. Thepressure relief channel 31 extends from the void 10, to a periphery 6 aof the polishing pad 3. More particularly, the pressure relief channel31 extends from the void 10, to a periphery 6 a of the adhesive 6.Hence, pressure that is generated in the void 10 during the polishingoperation may be evacuated through inlet 31 a and outlet 31 b ofpressure relief channel 31. In other words, any pressure that isgenerated in void 10 does not materially affect the transparent window14 since the pressure escapes through the pressure relief channel 31.Therefore, the transparent window 14 is not stressed or deformed due tothe pressure build-up and accurate end-pointing is facilitated,including reduced defectivity and wafer slippage.

Referring now to FIG. 4, there is provided another embodiment of apolishing pad having a pressure relief channel of the present invention.Similar features as in FIG. 1 are denoted by the same numerals. Here, apolishing pad 5 is provided comprising a pressure relief channel 51,having an inlet 51 a and an outlet 51 b, formed in the bottom layer 2.The pressure relief channel 51 extends from the void 10, to a periphery2 a of the polishing pad 5. More particularly, the pressure reliefchannel 51 extends from the void 10, to a periphery 2 a of the bottomlayer 2. Hence, pressure that is generated in the void 10 during thepolishing operation may be evacuated through inlet 51 a and outlet 51 bof pressure relief channel 51. In other words, any pressure that isgenerated in void 10 does not materially affect the transparent window14 since the pressure escapes through the pressure relief channel 51.Therefore, the transparent window 14 is not stressed or deformed due tothe pressure build-up and accurate end-pointing is facilitated.

Accordingly, the present invention provides a chemical mechanicalpolishing pad having reduced stress windows. In addition, the presentinvention provides a chemical mechanical polishing pad comprising, awindow formed in the polishing pad, the window having a void provided ona side thereof. The polishing pad further comprises a pressure reliefchannel provided from the void to a periphery of the polishing pad torelieve undue stress on the window. In addition, a membrane is providedin the channel to prevent contamination of the void. Also, the pressurerelief channel may be formed in the adhesive layer or the bottom layer.Similarly, one or more pressure relief channels may be formed in thepolishing layer, adhesive layer and the bottom layer together or anycombination thereof.

Additionally, in an exemplary embodiment of the present invention, thetransparent material of window 14 is made from apolyisocyanate-containing material (“prepolymer”). The prepolymer is areaction product of a polyisocyanate (e.g., diisocyanate) and ahydroxyl-containing material. The polyisocyanate may be aliphatic oraromatic. The prepolymer is then cured with a curing agent. Preferredpolyisocyanates include, but are not limited to, methlene bis 4,4′cyclohexylisocyanate, cyclohexyl diisocyanate, isophorone diisocyanate,hexamethylene diisocyanate, propylene-1,2-diisocyanate,tetramethylene-1,4-diisocyanate, 1,6-hexamethylene-diisocyanate,dodecane-1,12-diisocyanate, cyclobutane-1,3-diisocyanate,cyclohexane-1,3-diisocyanate, cyclohexane-1,4-diisocyanate,1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane, methylcyclohexylene diisocyanate, triisocyanate of hexamethylene diisocyanate,triisocyanate of 2,4,4-trimethyl-1,6-hexane diisocyanate, uretdione ofhexamethylene diisocyanate, ethylene diisocyanate,2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylenediisocyanate, dicyclohexylmethane diisocyanate, and mixtures thereof.The preferred polyisocyanate is aliphatic. The preferred aliphaticpolyisocyanate has less than 14% unreacted isocyanate groups.

Advantageously, the hydroxyl-containing material is a polyol. Exemplarypolyols include, but are not limited to, polyether polyols,hydroxy-terminated polybutadiene (including partially/fully hydrogenatedderivatives), polyester polyols, polycaprolactone polyols, polycarbonatepolyols, and mixtures thereof.

In one preferred embodiment, the polyol includes polyether polyol.Examples include, but are not limited to, polytetramethylene etherglycol (“PTMEG”), polyethylene propylene glycol, polyoxypropyleneglycol, and mixtures thereof. The hydrocarbon chain can have saturatedor unsaturated bonds and substituted or unsubstituted aromatic andcyclic groups. Preferably, the polyol of the present invention includesPTMEG. Suitable polyester polyols include, but are not limited to,polyethylene adipate glycol, polybutylene adipate glycol, polyethylenepropylene adipate glycol, o-phthalate-1,6-hexanediol, poly(hexamethyleneadipate) glycol, and mixtures thereof. The hydrocarbon chain can havesaturated or unsaturated bonds, or substituted or unsubstituted aromaticand cyclic groups. Suitable polycaprolactone polyols include, but arenot limited to, 1,6-hexanediol-initiated polycaprolactone, diethyleneglycol initiated polycaprolactone, trimethylol propane initiatedpolycaprolactone, neopentyl glycol initiated polycaprolactone,1,4-butanediol-initiated polycaprolactone, PTMEG-initiatedpolycaprolactone, and mixtures thereof. The hydrocarbon chain can havesaturated or unsaturated bonds, or substituted or unsubstituted aromaticand cyclic groups. Suitable polycarbonates include, but are not limitedto, polyphthalate carbonate and poly(hexamethylene carbonate) glycol.

Advantageously, the curing agent is a polydiamine. Preferredpolydiamines include, but are not limited to, diethyl toluene diamine(“DETDA”), 3,5-dimethylthio-2,4-toluenediamine and isomers thereof,3,5-diethyltoluene-2,4-diamine and isomers thereof, such as3,5-diethyltoluene-2,6-diamine,4,4′-bis-(sec-butylamino)-diphenylmethane,1,4-bis-(sec-butylamino)-benzene, 4,4′-methylene-bis-(2-chloroaniline),4,4′-methylene-bis-(3-chloro-2,6-diethylaniline) (“MCDEA”),polytetramethyleneoxide-di-p-aminobenzoate, N,N′-dialkyldiamino diphenylmethane, p,p′-methylene dianiline (“MDA”), m-phenylenediamine (“MPDA”),methylene-bis 2-chloroaniline (“MBOCA”),4,4′-methylene-bis-(2-chloroaniline) (“MOCA”),4,4′-methylene-bis-(2,6-diethylaniline) (“MDEA”),4,4′-methylene-bis-(2,3-dichloroaniline) (“MDCA”),4,4′-diamino-3,3′-diethyl-5,5′-dimethyl diphenylmethane,2,2′,3,3′-tetrachloro diamino diphenylmethane, trimethylene glycoldi-p-aminobenzoate, and mixtures thereof. Preferably, the curing agentof the present invention includes 3,5-dimethylthio-2,4-toluenediamineand isomers thereof. Suitable polyamine curatives include both primaryand secondary amines.

In addition, other curatives such as, a diol, triol, tetraol, orhydroxy-terminated curative may be added to the aforementionedpolyurethane composition. Suitable diol, triol, and tetraol groupsinclude ethylene glycol, diethylene glycol, polyethylene glycol,propylene glycol, polypropylene glycol, lower molecular weightpolytetramethylene ether glycol, 1,3-bis(2-hydroxyethoxy) benzene,1,3-bis-[2-(2-hydroxyethoxy) ethoxy]benzene,1,3-bis-{2-[2-(2-hydroxyethoxy) ethoxy]ethoxy}benzene, 1,4-butanediol,1,5-pentanediol, 1,6-hexanediol, resorcinol-di-(beta-hydroxyethyl)ether, hydroquinone-di-(beta-hydroxyethyl) ether, and mixtures thereof.Preferred hydroxy-terminated curatives include 1,3-bis(2-hydroxyethoxy)benzene, 1,3-bis-[2-(2-hydroxyethoxy) ethoxy]benzene,1,3-bis-{2-[2-(2-hydroxyethoxy) ethoxy]ethoxy}benzene, 1,4-butanediol,and mixtures thereof. Both the hydroxy-terminated and amine curativescan include one or more saturated, unsaturated, aromatic, and cyclicgroups. Additionally, the hydroxy-terminated and amine curatives caninclude one or more halogen groups. The polyurethane composition can beformed with a blend or mixture of curing agents. If desired, however,the polyurethane composition may be formed with a single curing agent.

In a preferred embodiment of the invention, window 14 may be formed of,for example, polyurethanes, both thermoset and thermoplastic,polycarbonates, polyesters, silicones, polyimides and polysulfone.Example materials for window 14 include, but are not limited to,polyvinyl chloride, polyacrylonitrile, polymethylmethacrylate,polyvinylidene fluoride, polyethylene terephthalate,polyetheretherketone, polyetherketone, polyetherimide, ethylvinylacetate, polyvinyl butyrate, polyvinyl acetate, acrylonitrile butadienestyrene, fluorinated ethylene propylene and perfluoralkoxy polymers.

Referring now to FIG. 5, a CMP apparatus 20 utilizing the polishing padof the present invention, including the pressure relief channel withmembrane 12 (not shown) is provided. Apparatus 20 includes a wafercarrier 22 for holding or pressing the semiconductor wafer 24 againstthe polishing platen 26. The polishing platen 26 is provided with pad 1,including window 14, pressure relief channel 11 and membrane 12, of thepresent invention. As discussed above, pad 1 has a bottom layer 2 thatinterfaces with the surface of the platen 26, and a polishing layer 4that is used in conjunction with a chemical polishing slurry to polishthe wafer 24. Note, although not pictured, any means for providing apolishing fluid or slurry can be utilized with the present apparatus.The platen 26 is usually rotated about its central axis 27. In addition,the wafer carrier 22 is usually rotated about its central axis 28, andtranslated across the surface of the platen 26 via a translation arm 30.Note, although a single wafer carrier is shown in FIG. 5, CMPapparatuses may have more than one spaced circumferentially around thepolishing platen. In addition, a transparent hole 32 is provided in theplaten 26 and overlies the void 10 and the window 14 of pad 1.Accordingly, transparent hole 32 provides access to the surface of thewafer 24, via window 14, during polishing of the wafer 24 for accurateend-point detection. Namely, a laser spectrophotometer 34 is providedbelow the platen 26 that projects a laser beam 36 to pass and returnthrough the transparent hole 32 and high transmission window 14 foraccurate end-point detection during polishing of the wafer 24.

Accordingly, the present invention provides a chemical mechanicalpolishing pad having reduced stress windows. In addition, the presentinvention provides a chemical mechanical polishing pad comprising, awindow formed in the polishing pad, the window having a void provided ona side thereof. The polishing pad further comprises a pressure reliefchannel provided from the void to a periphery of the polishing pad torelieve undue stress on the window. In addition, a membrane is providedin the channel to prevent contamination of the void. Also, the pressurerelief channel may be formed in the adhesive layer or the bottom layer.Similarly, one or more pressure relief channels may be formed in thepolishing layer, adhesive layer and the bottom layer together or anycombination thereof.

1. A chemical mechanical polishing pad comprising: a window formed inthe polishing pad, the window having a void provided on a side thereof;a pressure relief channel provided in the polishing pad from the void toa periphery of the polishing pad; and a membrane provided in the channelto prevent contamination of the void.
 2. The polishing pad of claim 1wherein the membrane is selected from the group comprising polyester,polyethylene, polypropylene, fluoropolymers, polyurethane foamed films,silicone, nylon, silk, woven materials and polyethylene terephthalate.3. The polishing pad of claim 2 wherein the membrane ispolytetrafluoroethylene.
 4. The polishing pad of claim 3 wherein themembrane is expanded polytetrafluoroethylene.
 5. The polishing pad ofclaim 1 wherein the pressure relief channel has a width between 0.70 mmto 6.50 mm.
 6. The polishing pad of claim 5 wherein the width variesbetween the void to the periphery of the polishing pad.
 7. The polishingpad of claim 1 wherein the pressure relief channel has a depth between0.38 mm to 1.53 mm.
 8. A chemical mechanical polishing pad comprising: apolishing layer having a window formed therein, the window being exposedto a void on a side thereof; a pressure relief channel provided in thepolishing layer from a portion of the void-exposed side of the window toa periphery of the polishing layer; and a membrane provided in thechannel to prevent contamination of the void.
 9. A chemical mechanicalpolishing pad comprising: a polishing layer overlying a bottom layer,and an adhesive layer disposed between the polishing layer and thebottom layer; a window formed in the polishing layer, the window beingexposed to a void on a side thereof; a pressure relief channel providedin the adhesive layer from the void to a periphery of the adhesivelayer; and a membrane provided in the channel to prevent contaminationof the void.
 10. A chemical mechanical polishing pad comprising: apolishing layer overlying a bottom layer, and an adhesive layer disposedbetween the polishing layer and the bottom layer; a window formed in thepolishing layer, the window being exposed to a void on a side thereof; apressure relief channel provided in the bottom layer from the void to aperiphery of the bottom layer; and a membrane provided in the channel toprevent contamination of the void.